Tourists frequently flock to Lizard Island, off the northeastern coast of Australia, to marvel the Great Barrier Reef. Among the dugongs, sea turtles, and jewel-toned corals, though, there’s another organism that doesn’t get nearly as much credit as it deserves: seagrass.
In fact, a team of Australian scientists has discovered that seagrasses of the Great Barrier Reef are absorbing climate-warming carbon dioxide from the atmosphere at a surprisingly high rate rate. In particular, the reef’s deepwater seagrass beds, spanning a region approximately the size of Switzerland, are a carbon-removal powerhouse, perhaps locking away up to 30 million tons of the stuff around the Great Barrier Reef, according to a new study.
This reef-bound carbon sink is one of many so-called “Blue Carbon” sinks. These are aquatic and marine environments which effectively store carbon, helping to mitigate climate change. Other such carbon sinks include marshes and mangrove forests.
The study, led by researchers from Deakin University and James Cook University and published in Biology Letters on December 12, measured the carbon contained in sediment cores taken from at a total of 19 sites along the northern section of the Great Barrier Reef. These sites represented three different depths: shallow, mid, and deep. The deepest seagrasses lie at nearly 24.38m.
The data showed that beds of the seagrass Halophila draw down about the same amount of carbon at depth as they do in shallower regions — a result the team was not expecting, per the study. Deepwater seagrass habitats held about nine times the amount of organic carbon as the bare sediment around them.
Extrapolating their measurements to the entire estimated deep-water Halophila habitat, they arrived at roughly 30 million tons of stored carbon.
“This is a really good news story,” Deakin University Marine Science Professor Peter Macreadie and study author told SBS News.
The study is clear that deeper sediment core samples and more variety in seagrass species would further support its findings. But overall, it’s clear the seagrass living along the Great Barrier Reef are helping save their very ecosystem.
Climate change is one of the greatest threats to coral reefs, with many corals expelling the algae that provide their food when the water is too warm. This causes them to bleach, a process that can eventually kill corals. Ocean acidification, also a result of carbon dioxide building up in our atmosphere, is another threat to reefs worldwide.
These seagrasses are helping stave off more destruction by keeping ocean warming and ocean acidifying carbon locked away. Unfortunately, erosion and pollution from development are killing seagrass meadows around the world.
In fact, 7 per cent of their habitat area is lost a year, according to the International Union for Conservation of Nature (IUCN). The Indo-Pacific, where Lizard Island is located, has the highest diversity of seagrass species in the world, but they’re still declining, per the IUCN.
Losing this seagrass could release its carbon into the atmosphere at a time when we need to remove carbon, not add any more.